The biological effects on eukaryotic cells of low doses of ionizing radiation are to be investigated within the framework of a biophysical theory. The determination of certain parameters should permit extrapolation of the dependence of cellular effects to doses too low for experimental determination. Modifications of the dose response curves by environmental factors such as oxygen tension and sensitizing drugs are an important related objective of investigation. In addition to intrinsic scientific significance, the results of this research are of pragmatic value in radiation protection and radiotherapy. A variety of radiations are to be applied including neutrons of a wide range of energies, x and gamma rays, alpha radiation and energetic ions up to Z equals 18. The higher organisms irradiated will be principally mammals but insects and plants are to be used in certain studies. The effects under investigation include carcinogenesis, cell transformation, chromosome aberrations and genetic impairment.